A PGF2a analogue (Z)-7-[(1R,2R,3R,5S)-3,5-dihydroxyl-2-[(E,3S)-3-hydroxyl-5-phenylpent-1-enyl]cyclopentyl]-N-ethylhept-5-eneamide (Bimatoprost) has been used for reducing intraocular pressure of patients suffering from open-angle glaucoma and ocular hypertension who can not tolerate or are not sensitive enough to other ocular hypotensive agents. Meanwhile, the analogue also has good application prospects in cosmetology. US2007282006A1 has reported that Bimatoprost has the function of promoting growth of eyelashes and hair, and WO2007111806A2 has reported that Bimatoprost has the function of weight reduction. Patents such as U.S. Pat. Nos. 7,166,730B2, 7,157,590B2 and WO2005058812 have detailedly reported a synthesis method of the compound, but research on crystalline forms of the compound has been little reported, and only US2009/016359A1 disclosed a crystalline form (referred to as a crystalline form B, see FIG. 1), the characteristic peaks where diffraction angles 2θ are 5.4, 6.2, 10.9, 11.3, 13.7, 16.6, 17.5, 18.3, 18.6, 18.9, 19.4, 19.7, 19.9, 20.7, 20.9, 21.6, 22.7 and 28.2 in the X-ray powder diffraction (XRPD) pattern of which.
The crystalline form of Bimatoprost in the prior art is insoluble in solvents such as ethyl acetate, tert-butyl acetate, dichloromethane and methyl isobutyl ketone etc. at low temperature, thus when Bimatoprost of the crystal morphology in the prior art is crystallized, it is dissolved at the temperature near the boiling point or boiling temperature of the solvents and then cooled for recrystallization. For example, US2009/016359A1 provided a method for preparing the crystalline form B, wherein the crystalline form B is mainly prepared by dissolving Bimatoprost in a single solvent such as ethyl acetate, tert-butyl acetate, dichloromethane, methyl isobutyl ketone, toluene, acetonitrile, diethyl ether, n-heptane and methyl tertiary butyl ether, or a mixed solvent of these solvents and esters (diethyl ether, methyl tertiary butyl ether and isopropyl ether) at the temperature near the boiling point or boiling temperature, and then cooling for recrystallization. However, it is unfavorable for stability of Bimatoprost, wherein the higher the temperature, the easier the Bimatoprost is degraded, so a method for performing crystallization after dissolution at lower temperature is necessary.